For speed control and position control for a system driven by a motor, there are a “voltage control method” of generating a voltage command directed to the motor based on a deviation between a command and an actual value, and a “current control method” of feeding back an actual current flowing through a winding of the motor so as to control the actual current to coincide with a current command.
The latter current control method applies the control forcedly overcoming the inductance component of the motor windings, and a current lag due to the inductance component in a control bandwidth of a current control system can thus be neglected, thereby providing stable torque control from a low speed range to a high speed range of the motor. On the other hand, in the voltage control method, the influence of the current lag due to the inductance component of the motor windings with respect to the voltage command cannot be neglected and the torque tracking characteristic is deteriorated compared to the current control method, resulting in a defect of presenting an oscillatory response.
By the way, as prior art, there is a technology, in which when an output DUTY is set in accordance with a required DUTY based on a required current for a torque motor for controlling an operation state in an actuator control device for an internal combustion engine, in order to avoid a case in which the output DUTY corresponding to the required DUTY cannot be set due to a restriction on a circuit and the like, the required DUTY and the output DUTY are made coincident with each other by converting the output DUTY into an output current in accordance with a power supply voltage and a resistance in a current path, further estimating a counter electromotive force using an estimated current smoothed in accordance with the coil inductance component of the torque motor, and adding the counter electromotive force to the required DUTY (refer to Patent Literature 1, for example).
Moreover, for a valve of a torque balance drive type which opens/closes the valve in a torque balance between a return spring by energizing means and a motor torque of a DC motor, there is a technology in which the DC motor is controlled by a combination of a feedforward control system and feedback control, and operation amounts of the feedforward control system and the feedback control are further corrected in accordance with a steady state deviation in position (refer to Patent Literature 2, for example).
According to the invention described in Patent Literature 1, it is expected that the lag of the actuator be eliminated, resulting in an increase in stability of the tracking characteristic.
Moreover, according to the invention described in Patent Literature 2, it is expected that the feedforward control system always apply the drive voltage for generating a motor torque corresponding to the return torque in accordance with the opening/closing directions of the valve, and the feedback control system (PID control described in Patent Literature 2) act so as to compensate the position deviation amount thus generated between the present position and the target position, and vibration be thus prevented from occurring by reducing the feedback control amount independently of the opening/closing directions of the valve.
Further, according to the invention described in Patent Literature 2, it is expected that optimal control be provided in accordance with operation characteristics of the valve, which are changed by factors such as the environmental temperature, by correcting a drive duty calculated in accordance with the position deviation by the feedforward control system and a coefficient in an arithmetic operation unit of the feedback control system.